This invention relates generally to sealed batteries, and more particularly to a system and method for safely charging sealed batteries such as sodium/metal chloride batteries.
Sodium chloride (NaCl) in the cathode of a sodium/metal chloride battery is converted into sodium (Na) ions and M-Cl complex through a series of chemical and transport steps during charging of a sodium/metal chloride battery. The Na ions are transported out of the cathode through a solid ion-conducting electrolyte into the anode compartment. The corresponding anode volume must be large enough to accommodate complete charging of the cathode. The total anode volume is typically about 0.42 times the total cathode volume for typical cathode configurations. If the anode volume is less, the liquid Na will pressurize the anode and could cause failure of either the solid electrolyte or anode compartment.
Although techniques are known for avoiding overcharging in the anode compartment of a sodium/metal chloride battery, these known techniques generally rely on the use of active circuit elements that add cost and reduce the reliability of a corresponding charging control system.
In view of the foregoing, it would be advantageous to provide a system and method for preventing overcharging (too much Na) in the anode compartment of a sodium/metal chloride battery in a manner that is more cost effective and achieve higher reliability than techniques that employ active circuit elements. It would be beneficial if the system and method could be successfully applied to any sealed battery having a variable fluid level anode compartment.